Aclis sp. 1

Souza, Leonardo Santos De, Araújo, Tarciso Almeida De & Pimenta, Alexandre Dias, 2024, Taxonomic review of Aclis Lóven, 1846 (Gastropoda, Eulimidae) from Brazil with notes on other congeners from the western Atlantic and Saint Helena, Zootaxa 5433 (4), pp. 451-499 : 464-465

Aclis sp. 1

Fig. 6

Material examined. Brazil: Rio de Janeiro state: OP II sta. 44; MNRJ 33505 [2†].

Characterization. Shell tall, conical, reaching about 2.0 mm long, 0.9 mm wide, eight whorls, whitish.Protoconch conical, about 3.5 whorls, first whorl (embryonic) smooth, remaining whorls sculptured by microscopic sigmoid axial lines at small intervals. Teleoconch with slightly convex whorls, surface glossy presenting faint microscopical spiral striae and strong incremental scars with irregular intervals. Body whorl half the total length, base rounded; aperture wide, 60% of body whorl length, strongly expanded laterally, rounded anteriorly, acute posteriorly; outer lip thin, sinuous, strongly advanced close to distal area; inner lip thin, reflected. Umbilical fissure present.

Measurements. MNRJ 33505: 7 whorls; SL= 2.0 mm; BWL= 1.0 mm; AL= 0.6 mm; SW= 0.9 mm; AW= 0.5 mm.

Remarks. Aclis sp. 1 has a multispiral protoconch, with the first whorl (embryonic/protoconch I) smooth and the remaining whorls ornamented by microscopic sigmoid axial lines. This feature is not common in Aclis , but Aclis walleri Jeffreys, 1867 known from the North Atlantic and Aclis aurisparva Bertolaso & Garilli, 2009 from Pliocene deposits of Italy present a similar pattern of sculpture in the larval shell ( Bouchet & Warén 1986: fig. 736; Bertolaso & Garilli 2009: figs 1–5). This pattern of sculpture is more common in other eulimids like species of Batheulima F. Nordsieck, 1968 , Fuscapex Warén, 1981 and Niso Risso, 1826 , which also presents some patterns of brownish coloration in the larval shell ( Bouchet & Warén 1986). In Batheulima and Fuscapex , the presence of the sigmoid axial lines in the protoconch is variable, with species of the same genus showing a smooth surface ( Bouchet & Warén 1986). This type of sculpture is possibly rare in Aclis . Despite the atypical protoconch, Aclis sp. 1 fits the genus by the shell shape with convex whorls ( Fig. 6A ), presence of microscopic spiral striae at the teleoconch surface ( Fig. 6B ), shape of the aperture and presence of an umbilical fissure ( Fig. 6C ).

A distinction between protoconch I and II is indicative of planktotrophy ( Warén 1983). The remaining species studied here are probably non planktotrophic because, in general, they have a paucispiral protoconch with smooth surface, without the distinction between protoconch I and II ( Warén 1983). The paucity of informative characters in the larval shells of Aclis species limits the inference of the type of larval development.

The general shape of the species closely resembles A. sarissa , A. kanela and A. walleri . It can be distinguished from A. sarissa and A. kanela by the presence of microscopic sculpture in the larval shell. The teleoconch whorls of Aclis sp. 1 seems less convex than in A. walleri but based on limited material it is difficult to assess variation, pending further comparisons to distinguish Aclis sp. 1 as a new species or determining the occurrence of A. walleri in the southwestern Atlantic.

Figures

FIGURE 6. Aclis sp. 1: MNRJ 33505. A. Shell in frontal view. B. Apical whorls: double arrows indicate microscopic and sigmoid axial line at the protoconch surface, single bottom arrow indicate microscopic spiral striae at the teleoconch surface. C. Body whorl. Scale bars: A. 1 mm; B. 200 μm; C. 500 μm.